A fiber-reinforced composite material, especially a composite material in which carbon fibers are used as reinforcing fibers, is expected to be applied to applications of a vehicle requiring to be light-weighted due to its high specific strength and specific rigidity. In particular, in a case where a matrix resin is thermoplastic, the material is promising from the standpoint of productivity and recyclability.
Patent Document 1 discloses a method including, impregnating carbon fibers having a specific fiber length with a resin, forming a preform in a sandwich structure by using a composite material precursor (prepreg) in which two single carbon fibers intersect within a specific range, and then press-molding the preform. Here, as a specific example, there is provided a sheet-making method which employs a wet method in order to intersect two single carbon fibers within a specific range. However, in many cases, such a method may require a drying process or the like, thereby complicating a manufacturing process. Further, it is difficult to form a prepreg with a relatively large thickness. Then, a large number of layered sheets are required at the time of molding, thereby complicating a molding process.
Patent Document 2 discloses a sheet material for a fiber-reinforced composite shaped product in which a plurality of reinforcing fiber bundles are randomly placed in a thermoplastic resin as a matrix. Here, in a state where the reinforcing fiber bundles are pulled and aligned at a predetermined ratio, the thermoplastic resin covers the periphery of the fiber bundles or impregnates into the fiber bundles, and then the fiber bundles are cut to be formed as chopped strands. Further, in Patent Document 2, the sheet material is inserted into a mold and molded by hot press. In this method, since the fiber bundles are cut after being covered with or impregnated with the thermoplastic resin, the cut chopped strands have a certain width and their fiber orientation tends to be close to one direction. Thus, there is a problem in that a high isotropy is hardly achieved even if the chopped strands are uniformly dispersed to obtain a shaped product sheet.    Patent Document 1: Japanese Patent Laid-Open Publication No. 2010-235779    Patent Document 2: Japanese Patent Laid-Open Publication H10-316771